The present invention relates generally to imaging systems and more particularly to a temporal change method using dual or multi-energy decomposition images.
Imaging devices, such as X-ray machines, are widely used in both medical and industrial applications. Imaging devices often use temporal processing to track change in an object over time.
Temporal processing systems typically include the following general modules: acquisition storage module, segmentation module, registration module, comparison module, and reporting module. The input images are 1-D, 2-D, 3-D, derived, synthesized, or montaged, where multiple separate images from a single time point are combined to provide a larger composite, seamless image.
Detection of change in medical images of a patient, which are acquired at two different instances in time, has great potential for improving diagnosis. The advent of digital imaging allows computer-assisted detection and identification of these changes and the creation of a “dissimilarity image” containing the change information. This dissimilarity image can be read by a human controller or can become the input to an automated analysis device such as a CAD (computer assisted diagnosis) algorithm.
Temporal subtraction is a current temporal processing method wherein dissimilarity-images are calculated using a simple pixel-by-pixel subtraction of registered images. Simple subtraction, however, results in images with poor contrast, and is not substantially robust when the two initial images are acquired using different techniques.
For a temporal subtraction image, the resulting pixel values (and hence the displayed gray-levels) are proportional to the dissimilarity images acquired with temporal separation.
Input images are often registered and processed to compensate for several factors such as: the difference in positioning of the subject during the two image acquisitions, the difference in acquisition parameters, the difference in the bit resolution of the images, and the differences in any pre or post processing that may have been applied to the images.
Image comparison is a common task in a number of applications including temporal processing of mono-modality images (1-D, 2-D, 3-D, derived, synthesized, montaged). Current methods involve simple arithmetic operations conducted on these images, including subtraction or addition.
Another imaging method is dual-energy subtraction radiography, which includes the energy dependence of X-ray attenuation by different tissues. Energy subtraction is achieved through a rapid sequence of at least two exposures of different energy levels. Through the use of a decomposition algorithm, separate bone and soft tissue images are obtained.
Generally the following radiographs are generated from the aforementioned method: the standard (high energy) image, the low energy image, the soft tissue image, and the bone image. Individually, these images are useful for understanding spatial features in the soft tissue and bone, however they are not currently very useful for quantifying temporal changes.
The disadvantages associated with current, imaging systems have made it apparent that a new technique for quantifying temporal change is needed. The new technique should substantially increase the amount of information acquired from temporal processing. The present invention is directed to this end.